The invention relates to a method for improving measurement values of an inertial measurement system in accordance with the preamble to claim 1.
Such methods are used in inertial measurement systems that are currently widely used. For instance, they are used in regulation and control systems in which it is necessary to know the precise acceleration and angular speeds relative to an inertial coordinate system (fixed star system). Generally the earth-fixed system is used in a first approximation for the inertial reference system. Such measurement systems, also called inertial platforms, are used in very technically complex systems in the design and control of weapons or are employed in tilt regulation of high speed trains. Such systems will also soon be mass-produced as motor vehicles increasingly are equipped with airbags and side-impact protection and also with pitch and yaw stabilizers or navigation systems and use such systems to trigger and control these safety devices. Such devices are also required in the airline industry and naval engineering.
Thus, known from German Offenlegungsschrift 44 16 586 is a measurement system with angular speed and acceleration sensors and a computer unit, in which system the measurement values of the sensors are converted to output values that are related to an inertial coordinate system.
The sensors currently available for these measurement systems are still quite expensive when they have the necessary reliability and precision. Although sensors such as gyroscopes and accelerometers can be produced cost effectively as microelectronic components, when built-in they have substantial errors so that for constructing the measurement systems substantial production expenses, including the required alignment and compensation, are required to achieve acceptable error and offset tolerances.
It is therefore the object of the present invention to provide a method for improving the measurement values in which a measurement system built with inexpensive sensors for angular speeds and accelerations can be aligned and compensated in a simple manner.
This object is achieved by the features of claim 1.
The inventive method is particularly advantageous when employed in the manufacture of mass-produced articles since only limited personnel are required to set up the measurement system and the testing equipment. Complex mechanical alignment work is not necessary, nor are the alignment apparatus and aids required for such work. The inventive method is very suitable for a fully-automatic, economical in-process inspection of inertial measurement systems since it makes possible the use of simple sensors for angular speeds and accelerations that are inexpensive to produce and takes into account their production tolerances in the alignment or calibration of the measurement system so that the accuracy of the inertial measurement system is substantially improved thereby.
One of the most important requirements for the calibration or alignment of the sensors is the availability of calibration standards with great precision, that is, high accuracy of the absolute values for angular speed and acceleration as well as optimum reproducibility of excitation and angular position. For this, the measurement system is mounted on a precision rotary table, the axis of rotation of which is precisely horizontal. The assembly occurs such that coordinate axes of the measurement system and of the rotary table are parallel; parallel displacements are inconsequential for the result. Thus the measurement system can be subjected in a simple manner to two reference excitations. A dynamic excitation of the gyroscope by precise, constant rotation and a static excitation of the accelerometer can be realized in this simple manner by the gravitational acceleration.
The inventive method is also advantageously further developed in the subordinate claims.
It has proved advantageous for optimum testing, before the measurement on the rotary table, to perform measurement of the angular speed offset of the gyroscope and the acceleration offset of the accelerometer as a function of temperature, since these measurements are generally time-consuming.